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From "Robert Chansler (Created) (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HDFS-2535) A Model for Data Durability
Date Thu, 03 Nov 2011 17:25:32 GMT
A Model for Data Durability
---------------------------

                 Key: HDFS-2535
                 URL: https://issues.apache.org/jira/browse/HDFS-2535
             Project: Hadoop HDFS
          Issue Type: Task
          Components: documentation
            Reporter: Robert Chansler
            Assignee: Robert Chansler
         Attachments: LosingBlocks.xlsx

This is a statistical model considering data durability in HDFS in the presence of Data Node
failures. The attached spreadsheet considers the probability of losing a block with three
replicas in the case of uncorrelated failures of DNs. Also included is a section that looks
at the consequences of simultaneous failures. 

The model parameters reflect experience at Yahoo with a large cluster. But it is easy to change
the parameters in the spreadsheet. Number of replicas is not a easily adjusted parameter.
And while published reports (the Google papers) suggest that node failures are not really
uncorrelated, this does give some practical insight into HDFS durability.

I and others have quoted from this work in the past. I thought it good to make the details
conveniently available.

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